Project1S16
Contents |
Homework Assignment 1: Rendering Point Clouds
In this project the goal is to read a number of 3D point positions from a file and render them onto the screen.
Besides becoming familiar with the math involved in rendering 3D scenes, this project will get you familiar with the tools and libraries that will be your friends throughout the quarter. These will include GLFW and GLew. You are free to use any other graphics or window management library, however you must contact us first for approval, as we want to make sure that you are not using a library that does too much of the homework for you.
We recommend that you start by getting your development software ready. More information on this is here.
Reading 3D Points from Files
A point cloud is a 3D collection of points, representing a 3D object. These point clouds are often acquired by laser scanning, but can also be acquired with the Microsoft Kinect and special software, or by processing a large number of photographs of an object and using Structure from Motion techniques (see Microsoft Photosynth or Autodesk 123D Catc).
In this project we're going to render the points defined in OBJ files. Note that OBJ files are normally used to define polygonal models, but for now we're ignoring that and use the vertex definitions to render points, ignoring all connectivity data. OBJ files are 3D model files which store the shape of an object with a number of vertices, associated vertex normals, and connectivity information to form triangles. Wikipedia has excellent information on the OBJ file format. The file format is an ASCII text format, which means that the files can be viewed and edited with a any text editor, such as Notepad.
Write a parser for the vertices and normals defined in OBJ files. It should be a simple 'for' loop in which you read each line from the file, for instance with the fscanf command. Your parser does not need to do any error handling - you can assume that the files do not contain errors. Add the parser to the starter code.
Use your parser to load the vertices from the following OBJ files and treat them as point clouds:
The files provided in this project only use the following three data types (other OBJ files may support more): v for vertex, vn for vertex normal, f for face.
The general format for vertex lines is:
v v_x v_y v_z r g b
Where v_x, v_y, v_z are the vertex x, y, and z coordinates and are strictly floats.
The values r, g, b define the color of the vertex, and are optional (i.e. they will be missing from most files). Like the vertex coordinates, they are strictly floats, and can only take on values between 0.0 and 1.0.
All values are delimited by a single whitespace character.
The general format for normal is the same as for vertices, minus the color info.
In summary:
- v: 'vertex': followed by six floating point numbers. The first three are for the vertex position (x,y,z coordinate), the next three are for the vertex color (red, green, blue) ranging from 0 to 1. Example:
v 0.145852 0.104651 0.517576 0.2 0.8 0.4
- vn: 'vertex normal': three floating point numbers, separated by white space. The numbers are for a vector which is used as the normal for a triangle. Example:
vn -0.380694 3.839313 4.956321
Lines starting with a '#' sign are comments and should be ignored.
In this homework assignment, you only need to parse for vertices and vertex normals, which are those lines of the file starting with a 'v' and 'vn'.
Write your parser so that it goes through the OBJ file, line by line. It should read in the first character of each line and based on it decide how to proceed, i.e., ignore all lines which do not start with a 'v' or 'vn'. The vertex definitions can be read with the fscanf command. Here is an example:
FILE* fp; // file pointer
float x,y,z; // vertex coordinates
float r,g,b; // vertex color
int c1,c2; // characters read from file
fp = fopen("bunny.obj","rb"); // make the file name configurable so you can load other files
if (fp==NULL) { cerr << "error loading file" << endl; exit(-1); } // just in case the file can't be found or is corrupt
c1 = fgetc(fp);
c2 = fgetc(fp);
if (c1=='v') && (c2==' ')
{
fscanf(fp, "%f %f %f %f %f %f", &x, &y, &z, &r, &g, &b);
}
// read normal data accordingly
fclose(fp); // make sure you don't forget to close the file when done
Load all three models in at startup.
Rendering the Points with OpenGL
To display the vertices you loaded, use the provided starter code. It contains hooks for rendering points with OpenGL, which are ready for you to use. Change the Display callback and replace the call to render the cube to render the OBJ object - don't call cube.draw() but call the respective OBJ object's draw command.
Use function keys F1, F2 and F3 to display the three models, respectively. Only one 3D model should be displayed at a time.
Just like the cube spins during display, make your OBJ models spin as well.
The points should be colored with normal coloring: use the vertex normals you parsed from the file, and map them into the range of zero to one. The x coordinate of the normal should map to red, y to green, z to blue.
Manipulating the Points
Once a model has been loaded, support the following keyboard commands to manipulate it:
- 'x'/'X': move left/right by a small amount
- 'y'/'Y': move down/up by a small amount
- 'z'/'Z': move into/out of the screen by a small amount
- 's'/'S': scale down/up (about the model's center, not the center of the screen)
- 'o'/'O': orbit the model about the window's z axis by a small number of degrees per key press, counterclockwise ('o') or clockwise ('O'). The z axis crosses the screen in the center of the window.
- 'r': reset position, orientation and size
Tweak the values for changes in position and size so that you can manually center each OBJ model in the window and scale it to the size of the window during grading.
Note: keep the object spinning at all times during manipulation.
Rendering the Points without OpenGL
Next you need to write code to display the point cloud WITHOUT USING OPENGL. This is important: in this part of the project we're going to render into a block of memory which the starter code displays (using OpenGL).
This is going to require that you evaluate the complete vertex transformation: p' = D * P * C-1 * M * p
As part of the starter code comes a file called rasterizer.cpp which contains code to render a 2D RGB array into your window. Use this code and modify it to render your point models. The models have to be rendered in the same place as when you render them with OpenGL. You need to add support for a toggle button on the keyboard (use 't' for toggle) to switch between the two rendering modes.
In this rendering mode, do NOT use normal coloring but instead use depth coloring. Use the projected z value of each point to determine its color. In order to utilize the entire color range from 0 to 1 you need to normalize the z values by determining the minimum and maximum values across the 3D model. Note that this has to be done from scratch for each frame due to the rotation of the object. For colors use grey values, bright white should be used for the closest point, black for the farthest. Use a background color of your choice, as long as it's not one of the point colors or the default of green.
Extra Credit
TBD
